Max Planck Institute for Terrestrial Microbiology

The Institute's central task is to understand the way microorganisms work at the molecular, cellular and ecological level. Institute scientists are concerned, on the one hand, with getting to the bottom of the metabolic diversity of microorganisms. On the other hand, they analyse the mechanisms that enable microorganisms to adapt to changing environmental influences and to modify themselves accordingly. Furthermore, the scientists investigate how the organisms regulate their cell structure and their reproduction. They also study the biogeochemical processes responsible for the exchange of climatically-relevant trace gases. These analyses encompass all functional levels, from the atomic and structural level to the molecular and cellular level, through to biochemistry and physiology, microbial communities and the association of microorganisms with plants.

Over 50 million genes and 40,000 proteins: combing through international databases for likely candidates, Tobias Erb and his colleagues at the Max Planck Institute for Terrestrial Microbiology in Marburg were faced with an overwhelming choice. In the end, the scientists picked out just 17 enzymes for the first synthetic metabolic pathway that is able to convert carbon dioxide into other organic molecules. Now they have to show that the cycle they sketched out on the drawing board also works in living cells.

Methane is an end product of anaerobic degradation of organic materials and is a potent greenhouse gas. Roughly, half of the world-wide methane emission is biologically performed by methanogenic archaea. We are interested in the enzymes involved in hydrogenotrophic methanogenesis. Here, we report on the crystal structure of the formyl-methanofuran dehydrogenase (Fwd) and heterodisulfide-reductase/hydrogenase complexes (Hdr/Mvh). These enzyme complexes are involved in the sequential reactions of ferredoxin reduction and CO2-reduction/fixation within the methanogenic pathway.

The conversion of the greenhouse gas carbon dioxide (CO2) into organic compounds is a key process in the global carbon cycle. In the past years, several novel pathways and enzymes for the conversion of CO2 were discovered in microorganisms. In parallel to these discoveries, new approaches were followed by using the methods of synthetic biology to establish artificial pathways for the fixation of CO2 that are more efficient compared to naturally existing CO2-fixation pathways. Synthetic CO2-fixation could pave the way towards novel applications in biotechnology and nanotechnology.

Many bacterial species colonize surfaces and form dense three-dimensional structures, known as biofilms, which are resistant to antibiotics and constitute one of the major forms of bacterial biomass on Earth. The developmental process that gives rise to biofilms is largely unknown. It was recently discovered that between the initial surface attachment and mature tower-shaped biofilm structures, the cellular architecture undergoes several critical transitions.

In clostridia the exergonic reduction of crotonyl-CoA to butyryl-CoA by NADH is coupled to the endergonic reduction of ferredoxin by NADH – a process called flavin-based electron bifurcation, catalyzed by a two-FAD-containing electron transferring flavoptrotein (Etf) and butyryl-CoA dehydrogenase (Bcd). This, and similar systems are wide-spread in anaerobic bacteria and archaea, which reduce ferredoxin for H2 formation in fermentations, for generation of ΔµNa+ via a ferredoxin-NAD reductase (Rnf) and in aceto-and methanogenesis for CO2 reduction by H2.

Hydrogen is an atmospheric trace gas which is mainly decomposed in soils. Already in the 1970s it was obvious that the decomposition process must be based on biological activity. However, it took more than 40 years until the decomposition process was finally understood. Today we know that nickel-iron hydrogenases of the group 5 are responsible for the oxidation of the atmospheric hydrogen. These hydrogenases are mainly found in Actinobacteria, e.g., Streptomyces or Mycobacterium, which are common microorganisms in soils.